Adding the new option log_allocator_stats_on_signal that will call
mallopt(M_LOG_STATS, 0), when a signal is sent to a process.
This call does not happen in the signal handler, but a variable
is set to trigger the mallopt call. The next time any allocation
call occurs, the mallopt call will be made.
Also, includes new unit tests for the new config option.
Test: All unit tests pass.
Test: Enabling the new feature and stop/start and sending the signal to
Test: a process and observing the log contains the memory stats.
Test: Did the above for a scudo and jemalloc based device.
Change-Id: Idcf6fca74036efb065b9c4cc037aaf9bcf0f139e
